Sonic Tool in a Single String Cased Borehole: - Fast Formation

This is a modelling guide to help you get started simulating Borehole Acoustic Measurement (Logging) systems in OnScale. In this initial example you will be shown how to get the dispersion plots using the symbol language

What is symbol?:Check out these articles to get more familiar with OnScale's scripting language symbol.

Note: This is not a MATLAB tutorial so there will be no instructions in this simulation guide in how to properly use the script. Upon download it will plot the dispersion spectra if all output data from the OnScale simulation is accounted for in the working directory

Model Description

The model we will show you how to build today will be a fluid-filled borehole surrounded by a fast or slow formation. A steel tool has been included in this model which will allow us to investigate the effects of interaction of steel pipe dispersion with that of the formation. A formation is characterised as fast or slow depending on whether its shear wave velocity is slower or faster than the compressional wave velocity in the borehole fluid.

The sonic measurement tool or in this case the pressure wave excitation will be located at the centre of borehole, the receivers will also be located along the centre of the borehole the first receiver will be placed 1.219m from the transmitter this will be referred to as the Tx-Rx spacing and the receivers are spaced periodically ever 0.152m the Rx-Rx spacing.

Download and Open the Model

OnScale Input Files have the file extension *.flxinp. To open the downloaded file:

Open OnScale

Select Analyst Mode

Select the Menu button in the top left of the application

Select Open

Preview Model

Preview model is used to view the geometry dimensions and material assignment of a model to ensure the script is correct. To preview a model, select the Preview Model icon in the Home tab of the application ribbon.

Note: Preview model will display data from any grph commands that come before the prcs command. If you have more than one grph command, you can cycle through the graphics by continuously selecting Preview Model. To close the preview, select Stop Preview.

Run Model on Cloud

The cloud scheduler will look a little different you don't estimate when running a MPI sim you simply request the amount of RAM needed and run the simulation. The model is set up to run a 500 part simulation. 1 part = 1 CPU.

To run the model on the cloud, select the Run on Cloud button in the Home tab of the application and follow these steps:

Change Job Name (optional)

Number of parts being requested - must be changed in script

Select RAM needed, request 100GB

Click Run

Note: Any supported files will be automatically included in the scheduler if they are in the same directory

Download Results

From the Home tab, select the Storage icon

Select the Refresh icon to refresh storage

Select the Job Name from the dropdown menu

Select the Download button

Select Download All

Choose a directory to download the results to. These results will be stored in the folder: 3D_Sonic-YYYYMMDD-HHMMSS\1 where YYYYMMDD-HHMMSS is the current date and time.

Analyse Results

We post-processed all of our results in MATLAB, we can provide a MATLAB script that we used. This is not a MATLAB tutorial however so there will be no instructions from here on out but here is a what the processed results look like if the script is used correctly. These results are from the fast formation simulations. Included in the files provided is a folder 'utils' this should be added to the MATLAB path.

Note: For post-processing the waveforms for the dispersions plots we used the “SFK waveform transform” toolbox. This was NOT created by OnScale and it can be obtained from the MATHWORKs webpage. It is not optimal and we would recommend using a better dispersion algorithim.